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LTC6957-1 Additive Noise with 10 MHz, +5 dBm sine wave

Product Number: LTC6957-1

I'm currently designing a W-band synthesizer that needs excellent long-term stability, and as such requires exceptionally low close-in phase noise.

To be specific, we need this synthesizer to exhibit a stability as measured in Allan Deviation of 1E-14 at 1 second of averaging time. Converted to phase noise at 10 MHz, this amounts to 1 Hz offset noise lying at -145 dBc/Hz per my latest calculations.

I understand most conventional references will not be able to attain this level of noise, but my application will have access to a resonator with sufficient Q - my main issue is ensuring the synthesizer has lower added noise compared to this super oscillator. However, in order for the rest of the synthesizer to function, I need a method to convert a sine wave to a square wave (for use in referencing HMC699) without contaminating the noise in excess of this very low value of -145 dBc/Hz at 1 Hz offset from a 10 MHz carrier.

As far as I can tell, LTC6957-1 is one of the lowest noise sine wave-square wave converters that is commercially available, but the datasheet only provides additive noise for a 100 MHz carrier. If this additive noise were to be primarily timing jitter, and were to fall by 20*log10(10) = 20 dB for a carrier of 10 MHz, then the part may be usable for my application, but I have no proof that this will occur at present.

Before I setup a test capable of making this measurement, I thought it best to ask - has anyone had reason to make this manner of test and knows the additive noise I can expect for a carrier that is not 100 MHz? Or can one of the ADI engineers provide guidance as to what I should expect?